One element per cell rule

The one element per cell rule or “one element rule” dictates that only a single solid cell, tile, liquid or gas can occupy a cell at any given time. This rule has far-reaching consequences.

This rule is not immediately obvious because liquids texture on a cell don’t occupy the whole cell if a gas is located on the cell directly above it, to reflect that more liquid could occupy this cell until it reaches the limit per cell.

When there is a solid or a tile on the cell above, the liquid texture will show it occupying the whole cell even if the liquid doesn’t reach the limit per cell.

This rule also applies inside pipes and rails, where different elements cannot mix in the same packet.

This rule does not apply to items (debris, seeds, food, or anything else dropped on the floor).

Applications

 * Liquid Airlock: Gas cannot displace liquids. By having a narrow vertical space with a stagnating liquid (or several, by using liquid stacking), a liquid airlock can be artificially created that’s totally impervious to gas while allowing Dupe passing.


 * Liquid Stacking: Different liquids will never mix. Even very low amounts of liquids will stack on top of each other if they are allowed to form layers before stacking the next one. A common 3 height stack is Polluted Water / Water / Salt Water. Polluted Water will be placed at the bottom so that the liquid above it will prevent off-gassing.


 * Atmospheric filter: By using gas weights and small one cell openings, you can filter gas in the atmosphere. This principle is used by the Rodriguez SPOM design.


 * Mechanical filter: By having a small loop primed with a gas or liquid, clever use of pipe priority and a valve to ensure the loop is never depleted, you can create a mechanical filter: a contraption that only lets a specific gas or liquid through, without any power usage.


 * Overpressure: Buildings and geysers that have an overpressure limit will check against the element present on their Cell of Interest. This element can be a liquid or a gas. By using a low amount of liquid rather than a gas, you can bypass the overpressure limit of most buildings. This is what allows Infinite Storage as well as the Hydra SPOM design in particular.


 * Bead Pump : By also using liquid mechanics to form beads and tile-swapping rules, where liquids exchange place with gases rather than push them, you can create a liquid Bead Pump that will force gas upward at a very fast speed.


 * Escher Waterfall : Very similar to bead pumps, a similar usage of liquid mechanics allows to form Escher Waterfall, which allows moving liquids upward or compressing them.